The present invention relates generally to medical devices and associated methods of manufacture. More particularly, the present invention relates to the application of layers of material to the surface of medical devices.
In recent years there has been a great deal of interest in the development of devices which enable physicians to perform medical procedures in a way which is minimally invasive to the body of the patient. These devices have been utilized to access many sites in the human body. Examples include coronary vasculature, cerebral vasculature, peripheral vasculature, and the gastrointestinal tract. During the fabrication of these devices, it is frequently necessary to apply an overlaying material to the outer surface of a radial cylindrical device. Many examples of the need to apply overlaying materials to generally cylindrical medical devices may be found in devices which are utilized to assure that the heart is properly perfused with blood.
Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the walls of a blood vessel. Individual stenotic lesions may be treated with a number of minimally invasive medical procedures including angioplasty and atherectomy.
Angioplasty techniques typically involve the use of a balloon catheter and a guide catheter. During this procedure, the distal end of the guide catheter is typically inserted into the femoral artery located near the groin of the patient. The guide catheter is urged through the vasculature of the patient until its distal end is proximate the restriction. In many cases, the distal end of the guide catheter is positioned in the ostium of the coronary artery.
In order to determine the location of the distal tip of the catheter, a ring of radiopaque material may be disposed proximate the distal tip of the guide catheter. This ring of radiopaque material produces a relatively bright signal on a fluoroscopy screen, allowing the physician to xe2x80x9cseexe2x80x9d where the tip of the catheter is located relative to the patients anatomy. Radiopaque markers are one example of an element which may be fabricated by applying an overlaying material to a generally cylindrical medical device.
Once the guide catheter has been properly positioned, the balloon catheter may be fed through a lumen in the guide catheter. The balloon is advanced beyond the distal end of the guide catheter until it is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. The balloon catheter may also include a radiopaque ring to aid the physician in positioning the balloon proximate the restriction.
Because a wide range of sizes and styles of catheters are used in angioplasty procedures it is desirable that the different sizes be readily identifiable. Identifying marks may be placed on a catheter by applying a layer of marking material. The marking material may define alphabetic or numeric characters. Alternately, the color or shape of the material may be used as an identifier. Visual identifiers are an additional example of an element which may be fabricate by applying an overlaying material to a generally cylindrical medical device.
To prevent subsequent closure of the vessel in the restricted area (restenosis) after an angioplasty procedure, a physician may implant a stent. Stents are normally comprised of a generally cylindrical skeletal frame which includes openings and a lumen which extends longitudinally through the stent. A variety of processes are known for fabricating stents. A stent may consist of a plurality of filaments or fibers which are wound or braided together to form a continuous structure. Alternately, the skeletal frame of a stent may be formed by removing material from a tubular element using a laser cutting process. Two general types of stents are commonly used; self-expanding and balloon expandable. A stent may be comprised of any biocompatible material possessing the structural and mechanical attributes necessary for supporting a diseased vessel.
A stent may also include one or more layers of additional material overlying the skeletal frame. Examples of such materials include a drug release coating comprising a therapeutic substance in a polymeric carrier. Drug release coatings are an additional example of an element which may be fabricate by applying an overlaying material to a generally cylindrical medical device.
As mentioned above, individual stenotic lesions may also be treated with an atherectomy procedure. During an atherectomy procedure, a stenotic lesion is mechanically cut or abraded away from the blood vessel wall. A catheter used in an atherectomy procedure may include an ablating burr having an abrasive coating. This abrasive coating may be fabricated by applying a layer of material to a body member of the ablating burr. This abrasive material is an additional example of an element which may be fabricate by applying an overlaying material to a generally cylindrical medical device.
Percutaneous myocardial revascularization (PMR) is an additional procedure which may be performed to improve perfusion of the heart muscle. PMR is typically used in clinical situations where angioplasty and atherectomy may not achieve the desired results. As described above, angioplasty, and atherectomy procedures have both been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as angioplasty, and atherectomy impractical for some patients.
When techniques which treat individual lesion are not practical a technique know as percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. PMR was inspired in part by observations that reptilian heart muscles are supplied with oxygen primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within a heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenisis. In addition to promoting increased blood flow, it is also believed that PMR improves a patient""s condition through denervation. Denervation is the elimination of nerves. The creation of wounds during a PMR procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.
In a PMR procedure, hibernating heart tissue may be ablated using radio frequency energy. In this procedure radio frequency energy is delivered to the hibernating heart tissue using a catheter which includes one or more conductors, and one or more electrodes. These conductors and electrodes may be fabricated by applying one or more layers to the outer surface of a generally tubular member. For example, a conductive material such as gold may be applied to the generally tubular member to create electrodes, conductors, and or antennas. These electrically conductive elements are an additional example of an element which may be fabricate by applying an overlaying material to a generally cylindrical medical device. Yet another example of elements which may be fabricated by applying an overlaying material to a generally cylindrical medical device include elements adapted to provide desirable structural characteristics, for example, strain relief""s, walls of varying stiffness, etc.
The present invention relates generally to medical devices and associated methods of manufacture. More particularly, the present invention relates to the application of layers of material to the surface of medical devices. A system is disclosed which is capable of depositing material onto a workpiece.
In a presently preferred embodiment, the workpiece is a medical device having a generally cylindrical surface. Also, in a presently preferred method, the workpiece is coupled to a workpiece motion control system which is capable of moving workpiece. The workpiece motion control system may include one or more linear actuators and one or more rotary actuators.
A carrier is positioned in close proximity to the workpiece. The carrier is coupled to a carrier motion control system, which may include one or more linear actuators and one or more rotary actuators. Several embodiments of the carrier and the carrier motion control system are disclosed. In a presently preferred embodiment, the carrier comprises a substantially laser transparent substrate having a layer of writing material overlaying at least a portion of one surface. Also in a presently preferred embodiment, the writing material comprises a sacrificial layer and a projectile layer.
The system further includes a laser source which is capable of directing a laser beam. In a presently preferred embodiment, the laser source is stationary. In other possible embodiments, the laser source may be coupled to a laser motion control system which may include a plurality of linear actuators and a plurality of rotary actuators. The actuators of the laser motion control system may be used to position the laser source so that the laser beam eliminates a portion of the carrier. A system controller may be utilized to selectively activate and coordinate the laser source, the laser motion control system, the carrier motion control system, and the workpiece motion control system.
A catheter in accordance with the present invention may include a strain relief or a radiopaque marker disposed on one of its surfaces utilizing a method in accordance with the present invention. Other elements which may be deposited on the surface of a workpiece utilizing methods in accordance with the present invention include: visual markers, conductors, electrodes, and abrasive layers.
A method of applying material to a work surface in accordance with the present invention may begin with the step of coupling the workpiece to the workpiece motion system. The carrier may likewise be coupled to the carrier motion control system. The carrier may be positioned so that it is in close proximity to a surface of the workpiece. The laser motion control system may be used to position the laser source such that the laser beam illuminates a portion of the carrier and carrier is interposed between laser source and workpiece.
The system controller may be utilized to selectively activate the laser source, the laser motion control, the carrier motion control system, and the workpiece motion control system. Relative motion is selectively created between the carrier and the laser beam to provide a constant supply of writing material. Relative motion is selectively created between the workpiece and the laser beam to make new portions of the workpiece surface available to receive material.